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Earth Satellite First Orbits Moon Twice

Artist's conception of HGS-1 communications satellite between Moon and Earth
Hughes artist's conception of HGS-1 satellite between Moon and Earth
The communications satellite known today as HGS-1 and owned by Hughes Global Services arrived in geosynchronous "stationary" orbit over the Pacific Ocean on June 17, 1998, successfully completing an historic mission that sent it around the Moon twice to reposition it in a useful orbit.

HGS-1 was launched Christmas Day 1997. A malfunctioning rocket left the satellite in an unusable, highly elliptical orbit. Insurers declared it a total loss for its original purpose of providing communications and television services in Asia.

Hughes Global Services Inc. obtained title in April 1998 to the otherwise functional satellite. The company is a subsidiary of Hughes Space and Communications Company which had built the model HS-601HP satellite.

The high-powered HGS-1 satellite was designed to relay television and telecommunications across Asia. The satellite was to have been referred to as AsiaSat.

However, during its launch on Christmas Day, 1997, the rocket carrying HGS-1 malfunctioned. That left the satellite in an unusable, highly inclined, elliptical orbit, even though the satellite was fully functional. The satellite did not have enough power to boost itself into the proper orbit some 23,000 miles above Earth.

After the launch failure, the original purchaser of the spacecraft filed an insurance claim. The insurers declared the spacecraft a total loss for its original purposes. Hughes owns the satellite today.

Slingshot Power. Controllers in the Hughes Mission Control Center in El Segundo, California, decided to try something that had not been done before with a communications satellite.

Hughes engineers decided to use a "slingshot" technique in May 1998 to blast the crippled communications satellite out and around the Moon to correct its orbit around Earth.

Hughes diagram of HGS-1 communications satellite traveling between Moon and Earth
Hughes diagram of HGS-1 satellite traveling between Moon and Earth
Over a period of several weeks, they fired the satellite's on-board rocket motor several times to nudge it out of its highly elliptical orbit of 217 miles by 22,300 miles above Earth. Then, on May 7, they sent it on a nine-day round-trip to the Moon where it followed a three-dimensional, figure-8 path, using lunar gravity to hurl it back toward Earth.

The Moon is approximately one-quarter-million miles from Earth. The experimental maneuver used most of the 3,700 pounds of propellant fuel aboard the satellite. Back at Earth, HGS-1 assumes a circular orbit over the planet's equator.

The experiment was the first time a commercial satellite had traveled to the Moon. It also was the first time commercial operators had tried anything so extreme to bring a lost satellite back into a proper orbit around Earth.

Hughes orbital engineers devised the novel mission to salvage the satellite, using lunar gravity to improve the resulting orbit once the satellite returned to Earth.

A Space First. That flyby, in mid-May 1998, was the first commercial mission to the Moon. Encouraged by the precision of that mission, Hughes performed a second lunar rendezvous in June 1998 to further improve the orbit.

The second mission concluded June 17, 1998. At 11:29 a.m. PDT, Hughes satellite controllers fired the on-board motor for twelve minutes, which slowed the spacecraft enough to enter a circular orbit 22,300 miles (36,000 km) above the equator. HGS-1 will remain "parked" in a dormant state over the Pacific Ocean until Hughes finds customers for it.

For Sale. When Hughes obtained title to the satellite, it agreed to try to find revenue-producing uses for the satellite and to share profits with the insurers. "This is a real opportunity for someone to kick-start or augment their business with an in-orbit satellite, at less cost and time than it would take to contract and build their own satellite," said Ronald V. Swanson, HGS president. Even though HGS' primary business is packaging satellite communications services for governmental entities, it is actively seeking interest in the entire satellite as well.

Distance To The Moon. The Moon is about 250,000 miles away (402,000 km).

HGS-1 made its first swing around the Moon May 13. On May 16, as the satellite approached Earth, controllers slowed it down by firing the on-board rocket motor. This put the satellite into a 15-day orbit around Earth with an apogee -- the farthest distance from Earth -- of about 303,000 miles (488,000 km).

On June 1, controllers nudged the satellite into position for a second lunar flyby. It passed the Moon again on June 6, at a distance of nearly 21,300 miles (34,300 km) from the surface, which is about 5.5 times farther than the initial lunar encounter of 3,883 miles (6,200 km). A small firing of the rocket motor June 11 reoriented the satellite for its final orbit around Earth.

On June 14 at 9:15 a.m. PDT, controllers fired the motor for 46 minutes, and again for two minutes at 10:50 a.m. Those burns slowed HGS-1 and allowed it to fall into a 46-hour orbit ranging in altitude from 22,300 miles (36,000 km) to 51,000 miles (82,000 km).

On June 16, controllers performed a 28-minute burn at 7:29 a.m. PDT, putting it into a nearly circular 28-hour orbit. The June 17 burn captured it in a 24-hour, geosynchronous orbit, so that it will orbit Earth at the same speed that the planet rotates. It will stay at roughly the same spot above Earth, but will drift a few degrees north and south of the equator every day.

Who Is Hughes? Hughes Global Services is a subsidiary of Hughes Space and Communications Company (HSC), the world's leading manufacturer of geostationary commercial communications satellites. Scientists and engineers from both HGS and HSC are taking part in the mission. Both companies are units of Hughes Electronics Corporation. PanAmSat Corporation, of which Hughes Electronics is the majority owner, has been providing critical command and tracking support for the mission through its ground station in Fillmore, Calif.

Artist's conception of HGS-1 communications satellite rocket burn above Earth
Artist's conception of
HGS-1 communications satellite
rocket burn above Earth
Previous Gravity Assists? NASA had used gravity assists to send spacecraft away from Earth on interplanetary missions, but no one had ever tried that way to bring a communications satellite back into Earth orbit. The experiment was the first known lunar mission involving a communications satellite and the first mission financed by a non-governmental entity.

After the firing on May 7, the satellite reached a maximum speed of 24,000 mph to send it on a 6-day outbound trip. On May 13, it passed behind the Moon, coming as close as 5,000 miles above the lunar surface. With an assist from lunar gravity, it swung around the Moon, changed directions and headed off on a 3-day return trip to Earth. On May 16, satellite controllers began braking maneuvers to help the satellite settle into an orbit around the equator. The satellite was tracked during its flight using signals received at ground stations and images seen by optical telescopes around the globe.

Scientists and engineers at Hughes Space and Comm and its subsidiary, Hughes Global Services Inc. (HGS), devised the salvage mission using the Moon to move the satellite into a usable circular orbit around earth. Assisting with the HGS-1 problem solution were the U.S. Air Force Space Command, NASA's Goddard Space Flight Center, and EMBRATEL, a Brazilian company.

Hughes controllers fired the satellite's onboard rocket motor more than a dozen times during the nine-day flight. Each firing adjusted the course of the rocket. That technique might reduce costs or boost more payload in orbit during future space missions.

HGS-1 Is A Powerful Satellite HGS-1 was built to send TV signals throughout Asia, India, the Middle East, Australasia and the Commonwealth of Independent States, which is composed of 11 former Soviet republics. It has 44 high-power transponders (radio repeaters) in the so-called C-band and Ku-band.

Hughes said the satellite was fully functional and capable of covering more than a quarter of the Earth at any time. It had kept the satellite in a stowed and dormant state in orbit while engineers decided what to do with it.

Hughes funded the salvage mission and puts the satellite to work. The company does most of its business with governments and military customers, and says it will share the profits with the insurance underwriters.

Hughes Space and Comm, a unit of Hughes Electronics Corporation, has been building communications and scientific spacecraft and instruments for more than 35 years. It is considered the world leader in manufacturing commercial geostationary communications satellites. Hughes Global Services packages commercial satellite services for government and military customers. HGS also works with other Hughes Electronics companies to provide end-to-end solutions for underserved commercial markets.

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